Since an upper limit of signal frequency of a commercially available coaxial connector cable is 110 GHz, a waveguide is used to transmit a high frequency signal which exceeds 110 GHz. Further, in order to transmit a high frequency signal between a waveguide and a semiconductor chip, a microstrip line board is used to convert the signal in a planar transmission line. That is, a waveguide-microstrip line converter is used. Further, the semiconductor chip is mounted and connected to the microstrip line board by wire bonding or flip chip bonding.
For example, as illustrated in FIGS. 5A and 5B, a microstrip line board 102 is mounted in a space connected to a waveguide 101 in a metal case 100, to protrude into the waveguide 101. Further, a semiconductor chip 103 is mounted and connected to the microstrip line board 102 by wire bonding or flip chip bonding.
However, in the configuration illustrated in FIGS. 5A and 5B, since a high frequency signal is transmitted through the microstrip line and the wire bonding or the flip chip bonding, a high frequency characteristic significantly deteriorates when the high frequency signal is transmitted between the waveguide and the semiconductor chip.
For example, since the length of the microstrip line extending from the waveguide and the semiconductor chip is inevitably increased and the microstrip line is connected to the semiconductor chip by the wire bonding or the flip chip bonding, a signal loss caused by a line resistance is significant. Further, as the frequency of a transmitted signal becomes higher, the wavelength is shortened. Thus, when the length of the microstrip line to the semiconductor chip is one quarter or more of the wavelength, waveform deterioration is also caused by signal reflection. Therefore, the deterioration of the high frequency characteristic when the high frequency signal is transmitted between the waveguide and the semiconductor chip is significant.
The following are reference documents.
[Document 1] Japanese Laid-Open Patent Publication No. 2002-198712 and
[Document 2] Japanese Laid-Open Patent Publication No. H5-343904.